1. Field of the Invention
This invention relates to a torsion spring and, more particularly, to a novel torsion spring apparatus and method for fabricating and mounting a torsion spring.
2. The Prior Art
Torsion springs are well-known in the art and are used for numerous applications. The torsion spring derives its name from the characteristic of its being twisted or placed under torsion forces to create the spring action. One particular type of torsion spring is designed as an elongated coil spring with one end anchored to a fixed surface with the other end mounted to achieve movement around an axis. A support rod is mounted coaxially in the spring and serves as a stabilizer to prevent the spring from buckling excessively at the extremes of travel, while serving as the axis of rotation.
Conventionally, the ends of the torsion spring are secured to their respective mountings by use of a mounting apparatus usually consisting of a conical or cylindrical insert which is placed into each end of the spring. The last several coils of the torsion spring are secured to the insert with the result that the effective length (active coils) of the spring is reduced by the number of coils (inactive coils) secured to the insert.
One specific application for a torsion spring is as a device to balance or compensate for the weight of an overhead, sectional door with the tension of the spring. Overhead sectional doors are found in commercial as well as residential applications and are customarily used as doors for wide entrances such as garages and the like. The overhead sectional door consists of a plurality of horizontal sections hingedly joined along abutting edges and are mounted in tracks at each end. The tracks are vertical at each side of the entrance into a horizontal section. The horizontal section supports the door overhead in a position horizontal to the floor. Therefore, the common name for the door is that of an overhead sectional door.
Clearly, of course, the entire weight of the door must be lifted vertically to open the door to place it in the horizontal overhead position. With most overhead sectional doors this weight can be substantial. It is, therefore, common to provide a coiled, torsion spring apparatus wherein the torsion spring is placed under sufficient tension to balance the weight of the overhead. The spring is under the greatest tension when the overhead sectional door is in the closed position and the least tension when the door is in the open position since very little weight of the door needs to be supported when the door is lifted to the horizontal position. Therefore, in order to provide the greatest service life to the torsion spring without exceeding the elastic limit of the spring material, it is desirable to have as many active coils of the torsion spring available for service as possible while providing the greatest possible anchor safety for the spring while it is under tension.
It would, therefore, be a significant advancement in the art to provide a novel torsion spring apparatus and method of fabrication wherein the conventional inserts are eliminated and the last coil of the torsion spring is configurated into the anchor mechanism for the torsion spring. Hard-drawn MB (Medium Bessemer) spring wire preferentially is used to fabricate smaller wire springs and, more particularly, the tightly bent anchor loops in the spring since oil tempered spring wire is more brittle and has a tendency to break when bent into short radius bends. Such a novel torsion spring apparatus and method of fabrication is disclosed and claimed herein.